It is known in the art to produce MEMS mirror assemblies by micromachining components from a single piece of silicon, for example. These assemblies have a central area containing the mirror or a platform designed to support a separate mirror and a pair of torsional hinges extending from the central mirror portion radially outward to an anchor frame or anchor pads which are used to attach the mirror to its mounting.
These mirrors are suitable for use to provide the repetitive modulating scans of a laser printer or the raster scan of a projection display. The reflective surface of the mirror may have many suitable shapes, such as oval, elongated or elliptical, rectangular, square or other suitable shape. The mirrors are designed such that the pivotal resonance of the mirror about its torsional hinges matches the selected scanning frequency for the mirror. Thus, by designing the mirror hinges so that the mirror resonates at this selected frequency, the scanning beam sweep can be produced using only a small amount of energy to maintain the resonance.
It has been be found experimentally that the stress loading of attaching the bracket to the using device stresses the piezoelectric drive elements and causes a shift in the resonant frequency of the mirror assembly and drive and/or a change in the amplitude response so that much more power is required to drive the pivoting motion of the mirror, thus requiring a more robust driving circuit. The amount of power required to drive a piezoelectric can increase by ten fold, for example. The additional power required is significant in battery power devices. Furthermore, resonant frequency changes will affect the scanning of the image that is being projected.
Accordingly, there is a need for simple, inexpensive technique for reducing the stress loading on the piezoelectric devices which does not increase the size of the mounting bracket.